Liquid storage tanks, including vehicle fuel tanks and liquid fertilizer tanks, utilize various types of tank caps to close off the fill spout of the tanks. These tanks are normally vented in some manner to equalize the pressure within the tank, or to maintain a small positive pressure within the tank. In many applications, the tank caps serve as the tank vent as well as the tank closure element.
One type of fuel filler cap having a valve assembly therein is disclosed in U.S. Pat. No. 3,995,657, issued to E. L. Horrey on Dec. 7, 1976. In this patent, a filler cap has a channel which communicates with the interior of a tank and with the atmosphere. A valve seat is disposed within the channel and a ball type valve member is biased by a spring, a second larger ball member, and a pivot plate into engagement with the valve seat. The ball valve is in constant engagement with the valve seat, thus forming an air tight seal, and only moves away from the seat when pressure within the tank reaches a certain predetermined pressure lower than the atmospheric pressure.
Another type of liquid tank cap having an integral valve assembly is disclosed in U.S. Pat. No. 4,244,522, issued to D. R. Hartwig on Jan. 13, 1981. This patent discloses a plurality of liquid storage tanks which are interconnected by common bases. Each tank includes a vent structure carried in the upper portion of the tank. The vent structure includes a valve arrangement having a valve seat, a rubber ball valve, and a float for supporting the ball. The ball valve is capable of sealing the tank, or venting the tank, depending on the amount and type of liquid in the tank. However, should the tank become inclined or inverted, the ball valve may not prevent escape of liquid through the tank cap.
Each of the above-noted tank caps would appear to provide sealing and venting of the tanks during certain operational conditions. However, they all appear to be ineffective in providing an unpressurized vented tank which is desirably sealed against liquid leakage.
The present invention is directed to overcoming one or more of the problems as set forth above.